In general, natural tanning of skin is to make the skin dark brown. The darkening is caused by distribution of melanin in outer skin cells, which has been synthesized in melanocytes and released therefrom. As the brown skin by tanning looks healthy, young and elegant, many people including Europeans, and even young ladies in Korea recently, love tanned, brown skin.
Up to the present, a usual way for skin tanning was to expose one's body to sunlight naturally, or to artificial ultraviolet (UV) rays irradiated from a UV irradiating device.
However, exposure of skin to UV irradiation for a long time causes side-effects such as wide-aging of skins, that is wrinkles, thickening of outer skin tissue, denaturation of elastin protein and loss of skin elasticity, as well as skin burning, or causes melanoma, the skin cancer. In particular, a strong UV irradiation from sunlight is a matter of great anxiety because of the destruction of the ozone layer.
Thus, other tanning methods having no side-effect of UV irradiation have been studied. One of them is to dye skin by the use of dihydroxy acetone (DHA) (K. Laden et al., J. Soc. Cosmetic Chemist 16, 777-782 (1965); T. Kurz et al., Cosmetics & Toiletries 109, 55-61 (1994)1; or to increase the synthesis of melanin in melanocytes by using tyrosine, tyrosine and hydrolyzed collagen, tyrosine derivatives, or diacyl glycerol WAG) A. Muller, Cosmetics & Toiletries 107, 125-132 (1992); U.S. Pat. No. 5,352,403.
The earlier method (dyeing with DHA) did not give a natural tanning effect because the dyeing could not be prolonged.
Caesapinia sappan L. is a plant belonging to the bean family. The heartwood, excluding the bark and the peripheral part of lignin from the main stalk of Caesapinia sappan L., has been used as a Chinese herb medicine. According to "The Treasures of Eastern Medicine ()", Caesapinia sappan L. has been used for the promotion of blood circulation, alleviation of pain and treatment of bruises. Among the people, Caesapinia sappan L. has been used as a red dye. The coloring components of Caesapinia sappan L., brazilin and hematoxylin, have been used as a hairdye.